While for human beings selection unambiguously establishes a mental link between
the user and the target, the realization of such an association in the virtual world
is not trivial. Both user and target have a presence in the physical world—that is, the
user is a human being and the target is a physical object—but not necessarily in the
virtual world. Instead, there are digital counterparts in the virtual world that act as
the proxies of these objects. The virtual representation (presence) of the selection
means that these digital counterparts will exchange information. The amo unt of infor-
mation may vary—in some cases a single notification of selection may be sufficient; in
other cases complete addresses and even content may be passed. The commun ication
may have a single direction, either from pointer to target or vice versa, or be bidirec-
tional. The act of selection ends when the pointer and target counterparts have
exchanged sufficient information to establish an association. Note that actual knowl-
edge of selection may be on the side of the user or the target, or on both.
12.5.1 Implementing Pointing
Capturing the act of pointing requires the assistance of pointing devices and/or
pointing receptors that are able to detect the physical link established. A range of
technologies may be applied here, both active and passive. The actual action follow-
ing the selection may need different technologies and use different channels for
communication. Figure 12.4 is an overview of the components involved. Note that
some components may be combined in one device.
Pointing Device
Mental Link
Physical Link
Pointing Receptor
Virtual Link
Mental, physical, and virtual links in pointing.
12.5 Implementing Physical Selection 315

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